Trajectory setting device and trajectory setting method

ABSTRACT

A trajectory setting device that sets a trajectory of a host vehicle includes a first path generation unit configured to generate a first path by assuming all obstacles around the host vehicle to be stationary obstacles, a second path generation unit configured to generate a second path when the moving obstacle is assumed to move independently, a third path generation unit configured to generate a third path when the moving obstacle is assumed to move while interacting with at least one of the other obstacles or the host vehicle, a reliability calculation unit configured to calculate reliability of the second path and reliability of the third path, and a trajectory setting unit configured to set the trajectory for traveling from the first path, the second path, and the third path based on the reliability of the second path and the reliability of the third path.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of U.S. patentapplication Ser. No. 16/850,764 filed Apr. 16, 2020 (allowed), which isa continuation application of U.S. patent application Ser. No.15/945,395, filed on Apr. 4, 2018 (now U.S. Pat. No. 10,877,482 issuedDec. 29, 2020), in the U.S. Patent & Trademark Office, which is based onand claims priority under 35 U.S.C. § 119 to Japanese Patent ApplicationNo. 2017-076069, filed on Apr. 6, 2017, in the Japan Patent Office. Theentire disclosures of the prior applications are considered part of thedisclosure of the accompanying continuation application, and are herebyincorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a trajectory setting device and atrajectory setting method.

2. Description of Related Art

For example, Japanese Unexamined Patent Application Publication No.11-91397 (JP 11-91397 A) is known in the related art for a device thatperforms autonomous driving of a host vehicle. An autonomous travelingvehicle control device disclosed in JP 11-91397 A performs autonomousdriving (autonomous traveling) of the host vehicle based on the resultof detection of an external environment of the host vehicle.

SUMMARY

In order to perform autonomous driving of a host vehicle, candidates forpossible paths of the host vehicle need to be generated using a methodthat is set in advance in a control device and the like of the hostvehicle. A trajectory of the host vehicle for traveling needs to be setfrom the generated paths by considering traveling efficiency and thelike. However, the method set in advance in the control device and thelike for generating paths may be inappropriate according to thesituation of the host vehicle. In such a case, all paths generated usingthe method are inappropriate, and the trajectory of the host vehicle fortraveling may not be appropriately set from the paths.

In the present technical field, it is desirable to provide a trajectorysetting device and a trajectory setting method that can appropriatelyset a trajectory of a host vehicle for traveling from paths generatedusing a plurality of different methods.

A first aspect of the present disclosure relates to a trajectory settingdevice that sets a trajectory of a host vehicle for traveling. Thetrajectory setting device includes an obstacle recognition unitconfigured to recognize obstacles around the host vehicle, a first pathgeneration unit configured to generate a first path of the host vehicleby assuming all of the obstacles to be stationary obstacles, a movingobstacle detection unit configured to detect a moving obstacle from theobstacles, a second path generation unit configured to generate a secondpath of the host vehicle when the moving obstacle is assumed to moveindependently, a third path generation unit configured to generate athird path of the host vehicle when the moving obstacle is assumed tomove while interacting with at least one of the other obstacles or thehost vehicle, a reliability calculation unit configured to calculatereliability of the second path and reliability of the third path, and atrajectory setting unit configured to set the trajectory of the hostvehicle for traveling from the first path, the second path, and thethird path based on the reliability of the second path and thereliability of the third path.

The trajectory setting device according to the first aspect of thepresent disclosure generates the first path of the host vehicle when allof the obstacles are assumed to be stationary obstacles, generates thesecond path of the host vehicle when the moving obstacle is assumed tomove independently, and generates the third path of the host vehiclewhen the moving obstacle is assumed to move while interacting with atleast one of the other obstacles or the host vehicle. The trajectorysetting device calculates the reliability of the second path and thereliability of the third path, and sets the trajectory of the hostvehicle for traveling from the first path, the second path, and thethird path based on the reliability of the second path and thereliability of the third path. Thus, the trajectory setting device canappropriately set the trajectory of the host vehicle for traveling frompaths that are generated using a plurality of different methods.

In the trajectory setting device according to the first aspect of thepresent disclosure, when the reliability of the third path is higherthan or equal to a third reliability threshold, the trajectory settingunit may set the trajectory of the host vehicle for traveling from thethird path. When the reliability of the third path is lower than thethird reliability threshold, and the reliability of the second path ishigher than or equal to a second reliability threshold, the trajectorysetting unit may set the trajectory of the host vehicle for travelingfrom the second path. When the reliability of the third path is lowerthan the third reliability threshold, and the reliability of the secondpath is lower than the second reliability threshold, the trajectorysetting unit may set the trajectory of the host vehicle for travelingfrom the first path. The trajectory setting device can employ thetrajectory of the host vehicle for traveling in the order of the thirdpath and the second path when reliability is sufficiently high. When thereliability of the second path and the reliability of the third path arenot sufficiently high in the trajectory setting device, the trajectoryof the host vehicle for traveling is set from the first path. Thus, asituation where the trajectory of the host vehicle for traveling cannotbe set due to the insufficient reliability of the second path and theinsufficient reliability of the third path is suppressed.

In the trajectory setting device according to the first aspect of thepresent disclosure, the reliability calculation unit may calculate thereliability of the second path based on reliability of sensing of thehost vehicle and reliability of prediction of a candidate path of themoving obstacle when the moving obstacle is assumed to moveindependently. The trajectory setting device performs the calculationbased on the reliability of sensing of the host vehicle acquired fromthe state and the like of a sensor of the host vehicle, and thereliability of prediction of the candidate path of the moving obstaclewhen the moving obstacle is assumed to move independently. Thus, thetrajectory setting device can acquire the reliability of the second pathmore appropriately than when the reliability of the second path iscalculated from merely one of the reliability of sensing of the hostvehicle or the reliability of prediction of the candidate path of theindependent moving obstacle.

In the trajectory setting device according to the first aspect of thepresent disclosure, the reliability calculation unit may calculate thereliability of the third path based on reliability of sensing of thehost vehicle and reliability of prediction of a candidate path of themoving obstacle when the moving obstacle is assumed to move whileinteracting with at least one of the other obstacles or the hostvehicle. The trajectory setting device performs the calculation based onthe reliability of sensing of the host vehicle acquired from the stateand the like of the sensor of the host vehicle, and the reliability ofprediction of the candidate path of the moving obstacle when the movingobstacle is assumed to move while interacting with at least one of theother obstacles or the host vehicle. Thus, the trajectory setting devicecan acquire the reliability of the third path more appropriately thanwhen the reliability of the third path is calculated from merely one ofthe reliability of sensing of the host vehicle or the reliability ofprediction of the candidate path of the interactive moving obstacle.

A second aspect of the present disclosure relates to a trajectorysetting device that sets a trajectory of a host vehicle for traveling.The trajectory setting device includes an obstacle recognition unitconfigured to recognize obstacles around the host vehicle, a movingobstacle detection unit configured to detect a moving obstacle from theobstacles, a second path generation unit configured to generate a secondpath of the host vehicle when the moving obstacle is assumed to moveindependently, a third path generation unit configured to generate athird path of the host vehicle when the moving obstacle is assumed tomove while interacting with at least one of the other obstacles or thehost vehicle, a reliability calculation unit configured to calculatereliability of the second path and reliability of the third path, and atrajectory setting unit configured to set the trajectory of the hostvehicle for traveling from the second path and the third path based onthe reliability of the second path and the reliability of the thirdpath.

The trajectory setting device according to the second aspect of thepresent disclosure generates the second path of the host vehicle whenthe moving obstacle is assumed to move independently, and generates thethird path of the host vehicle when the moving obstacle is assumed tomove while interacting with at least one of the other obstacles or thehost vehicle. The trajectory setting device calculates the reliabilityof the second path and the reliability of the third path, and sets thetrajectory of the host vehicle for traveling from the second path andthe third path based on the reliability of the second path and thereliability of the third path. Thus, the trajectory setting device canappropriately set the trajectory of the host vehicle for traveling frompaths that are generated using a plurality of different methods.

A third aspect of the present disclosure relates to a trajectory settingmethod of setting a trajectory of a host vehicle to avoid obstacles. Thetrajectory setting method includes generating a first path of the hostvehicle by assuming all obstacles around the host vehicle to bestationary obstacles, generating a second path of the host vehicle whena moving obstacle detected from the obstacles is assumed to moveindependently, generating a third path of the host vehicle when themoving obstacle is assumed to move while interacting with at least oneof the other obstacles or the host vehicle, calculating reliability ofthe second path and reliability of the third path, and setting thetrajectory of the host vehicle from the first path, the second path, andthe third path based on the reliability of the second path and thereliability of the third path.

The trajectory setting method according to the third aspect of thepresent disclosure generates the first path of the host vehicle when allof the obstacles are assumed to be stationary obstacles, generates thesecond path of the host vehicle when the moving obstacle is assumed tomove independently, and generates the third path of the host vehiclewhen the moving obstacle is assumed to move while interacting with atleast one of the other obstacles or the host vehicle. The trajectorysetting method calculates at least the reliability of the second pathand the reliability of the third path, and sets the trajectory of thehost vehicle for traveling from the first path, the second path, and thethird path based on the reliability of the second path and thereliability of the third path. Thus, the trajectory setting method canappropriately set the trajectory of the host vehicle for traveling frompaths that are generated using a plurality of different methods.

In the trajectory setting method according to the third aspect of thepresent disclosure, in the setting of the trajectory, when thereliability of the third path is higher than or equal to a thirdreliability threshold, the trajectory of the host vehicle for travelingmay be set from the third path. In the setting of the trajectory, whenthe reliability of the third path is lower than the third reliabilitythreshold, and the reliability of the second path is higher than orequal to a second reliability threshold, the trajectory of the hostvehicle for traveling may be set from the second path. In the setting ofthe trajectory, when the reliability of the third path is lower than thethird reliability threshold, and the reliability of the second path islower than the second reliability threshold, the trajectory of the hostvehicle for traveling may be set from the first path. The trajectorysetting method can employ the trajectory of the host vehicle fortraveling in the order of the third path and the second path whenreliability is sufficiently high. When the reliability of the secondpath and the reliability of the third path are not sufficiently high inthe trajectory setting device, the trajectory of the host vehicle fortraveling is set from the first path. Thus, a situation where thetrajectory of the host vehicle for traveling cannot be set due to theinsufficient reliability of the second path and the insufficientreliability of the third path is suppressed.

In the trajectory setting method according to the third aspect of thepresent disclosure, in the calculating of the reliability, thereliability of the second path may be calculated based on reliability ofsensing of the host vehicle and reliability of prediction of a candidatepath of the moving obstacle when the moving obstacle is assumed to moveindependently. The trajectory setting method performs the calculationbased on the reliability of sensing of the host vehicle acquired fromthe state and the like of a sensor of the host vehicle, and thereliability of prediction of the candidate path of the moving obstaclewhen the moving obstacle is assumed to move independently. Thus, thetrajectory setting method can acquire the reliability of the second pathmore appropriately than when the reliability of the second path iscalculated from merely one of the reliability of sensing of the hostvehicle or the reliability of prediction of the candidate path of theindependent moving obstacle.

In the trajectory setting method according to the third aspect of thepresent disclosure, in the calculating of the reliability, thereliability of the third path may be calculated based on reliability ofsensing of the host vehicle and reliability of prediction of a candidatepath of the moving obstacle when the moving obstacle is assumed to movewhile interacting with at least one of the other obstacles or the hostvehicle. The trajectory setting method performs the calculation based onthe reliability of sensing of the host vehicle acquired from the stateand the like of the sensor of the host vehicle, and the reliability ofprediction of the candidate path of the moving obstacle when the movingobstacle is assumed to move while interacting with at least one of theother obstacles or the host vehicle. Thus, the trajectory setting methodcan acquire the reliability of the third path more appropriately thanwhen the reliability of the third path is calculated from merely one ofthe reliability of sensing of the host vehicle or the reliability ofprediction of the candidate path of the interactive moving obstacle.

As described thus far, according to the aspects of the presentdisclosure, the trajectory of the host vehicle for traveling can beappropriately set from paths that are generated using a plurality ofdifferent methods.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a diagram illustrating an autonomous driving system accordingto the present embodiment;

FIG. 2 is a flowchart illustrating a trajectory setting method;

FIG. 3 is a flowchart illustrating a third path generation process; and

FIG. 4 is a flowchart illustrating a candidate path selection process.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be describedwith reference to the drawings. A trajectory setting device according tothe present embodiment constitutes a part of an autonomous drivingsystem.

FIG. 1 is a diagram illustrating the autonomous driving system accordingto the present embodiment. An autonomous driving system 100 illustratedin FIG. 1 executes autonomous driving of a vehicle such as a passengercar. The autonomous driving is a vehicle control for the vehicle toautonomously travel toward a destination set in advance. The destinationmay be set by an occupant such as a driver, or may be automatically setby the autonomous driving system 100. In autonomous driving, the vehicleautonomously travels, and the driver does not need to perform a drivingoperation. Hereinafter, the vehicle that is a target for autonomousdriving in the autonomous driving system 100 will be referred to as ahost vehicle.

Configuration of Autonomous Driving System

As illustrated in FIG. 1 , the autonomous driving system 100 isconfigured to include a trajectory setting device 101. The trajectorysetting device 101 is a device that sets a trajectory of the hostvehicle for traveling in autonomous driving and the like.

The autonomous driving system 100 includes an electronic control unit(ECU) 10 that manages the entire system. The ECU 10 is an electroniccontrol unit that includes a central processing unit (CPU), a read-onlymemory (ROM), a random access memory (RAM), a controller area network(CAN) communication circuit, and the like. For example, the ECU 10realizes various functions through the CAN communication circuit byloading a program stored in the ROM into the RAM and executing theprogram loaded into the RAM by the CPU. The ECU 10 may be configuredwith a plurality of electronic units. The ECU 10 is connected to a GPSreceiver 1, an external sensor 2, an internal sensor 3, a map database4, an HMI 5, and an actuator 6.

The GPS receiver 1 measures the position of the host vehicle (forexample, the latitude and the longitude of the host vehicle) byreceiving signals from three or more GPS satellites. The GPS receiver 1transmits the measured position information of the host vehicle to theECU 10.

The external sensor 2 is a detector that detects a situation around thehost vehicle. The external sensor 2 includes at least one of a camera ora radar sensor. The camera is an imaging device that images the externalsituation of the host vehicle. The camera is disposed behind awindshield of the host vehicle. The camera transmits the imagedinformation related to the external situation of the host vehicle to theECU 10. The camera may be a monocular camera or a stereo camera. Thestereo camera includes two imaging units that are disposed to reproducebinocular disparity.

The radar sensor is a detector that detects an obstacle around the hostvehicle using an electric wave (for example, a millimeter wave) orlight. The radar sensor includes a millimeter wave radar or lightdetection and ranging (LIDAR). The radar sensor transmits an electricwave or light to the area around the host vehicle and detects anobstacle by receiving an electric wave or light reflected by theobstacle. The radar sensor transmits the detected obstacle informationto the ECU 10. The radar sensor may include both of a millimeter waveradar and LIDAR.

A traffic signal may be detected by the camera, and an external obstaclemay be detected using LIDAR. In such a case, the traffic signal may bedetected using template matching based on at least one of colorinformation (for example, brightness) of the image acquired by thecamera or the shape of the image (for example, using Hough transform).Map information described below may be used in order to improve theaccuracy of detection of the traffic signal.

The internal sensor 3 is a detector that detects the traveling state ofthe host vehicle. The internal sensor 3 includes a vehicle speed sensor,an acceleration sensor, and a yaw rate sensor. The vehicle speed sensoris a detector that detects the speed of the host vehicle. For example, awheel speed sensor that is disposed at a wheel of the host vehicle or adriveshaft rotating with the wheel as a single body and detects therotational speed of the wheel is used as the vehicle speed sensor. Thevehicle speed sensor transmits the detected vehicle speed information(wheel speed information) to the ECU 10.

The acceleration sensor is a detector that detects the acceleration ofthe host vehicle. For example, the acceleration sensor includes aforward and rearward acceleration sensor and a lateral accelerationsensor. The forward and rearward acceleration sensor detects the forwardand rearward acceleration of the host vehicle. The lateral accelerationsensor detects the lateral acceleration of the host vehicle. Forexample, the acceleration sensor transmits the acceleration informationof the host vehicle to the ECU 10. The yaw rate sensor is a detectorthat detects the yaw rate (rotational angular velocity) of the hostvehicle about the vertical axis at the center of gravity of the hostvehicle. For example, a gyrosensor can be used as the yaw rate sensor.The yaw rate sensor transmits the detected yaw rate information of thehost vehicle to the ECU 10.

The map database 4 is a storage device that stores the map information.For example, the map database 4 is formed in a hard disk drive (HDD)that is mounted in the host vehicle. The map information includesTraffic Rule Map. Traffic Rule Map is a map that associates a trafficrule with position information on the map. Traffic Rule Map includes alane and lane connection information.

The map information can include the output signal of the external sensor2 in order to use simultaneous localization and mapping (SLAM)technology. That is, the map information includes Localization Knowledgethat is used for recognizing the position of the host vehicle.Localization Knowledge is three-dimensional position data that links afeature point to coordinates. Examples of the feature point include apoint that exhibits a comparatively high reflectance in the detectionresult of LIDAR and the like, and a structure (for example, the exteriorof a sign, a pole, and a curb) that has a shape showing characteristicedges.

The map information may include Background Knowledge. BackgroundKnowledge is a map that uses voxels to represent a three-dimensionalobject present as an obstacle (stationary obstacle) which is stationaryand does not change in position on the map. The map information mayfurther include Traffic Light Location that is three-dimensionalposition data of the traffic signal.

The map information may include Surface Knowledge that is surface datarelated to the level of the surface. The map information may includeTrajectory Knowledge. Trajectory Knowledge is data that represents apreferable traveling trajectory defined on the road. LocalizationKnowledge, Background Knowledge, Traffic Light Location, SurfaceKnowledge, and Trajectory Knowledge may be stored in a storage devicedifferent from the map database 4.

The HMI 5 is an interface for inputting and outputting informationbetween the autonomous driving system 100 and the occupant. For example,the HMI 5 includes a display and a speaker. The HMI 5 outputs an imageon the display and outputs audio from the speaker in accordance with acontrol signal from the ECU 10. The display may be a head-up display.For example, the HMI 5 includes an input device (a button, a touchpanel, a voice input device, or the like) for receiving an input fromthe occupant.

The actuator 6 is a device that is used for controlling the vehicle. Theactuator 6 includes at least a throttle actuator, a brake actuator, anda steering actuator. The throttle actuator controls the drive power ofthe vehicle by controlling the amount of air supplied to an engine(throttle opening degree) in accordance with a control signal from theECU 10. When the vehicle is a hybrid vehicle, the drive power iscontrolled by inputting a control signal from the ECU 10 into a motor asa power source in addition to controlling the amount of air supplied tothe engine. When the vehicle is an electric vehicle, the drive power iscontrolled by inputting a control signal from the ECU 10 into a motor asa power source instead of the throttle actuator. In such cases, themotor as a power source constitutes the actuator 6.

The brake actuator controls braking power applied to the wheel of thevehicle by controlling a brake system in accordance with a controlsignal from the ECU 10. For example, a hydraulic brake system can beused as the brake system. The steering actuator controls, in accordancewith a control signal from the ECU 10, driving of an assist motor thatcontrols a steering torque in an electric power steering system.Accordingly, the steering actuator controls the steering torque of thevehicle.

A functional configuration of the ECU 10 will be described. The ECU 10includes a vehicle position recognition unit 11, an obstacle recognitionunit 12, a moving obstacle detection unit 13, a traveling staterecognition unit 14, a first path generation unit 15, a second pathgeneration unit 16, a third path generation unit 17, a reliabilitycalculation unit 18, a trajectory setting unit 19, a traveling plangeneration unit 20, and a traveling controller 21. A part of thefunctions of the ECU 10 may be executed in a server that can communicatewith the host vehicle.

The vehicle position recognition unit 11 recognizes the position of thehost vehicle on the map (host vehicle position estimation: localization)based on the position information of the host vehicle received by theGPS receiver 1 and the map information of the map database 4.Specifically, the vehicle position recognition unit 11 uses LocalizationKnowledge of the map database 4 and the detection result of the externalsensor 2 to recognize the position of the host vehicle using SLAMtechnology. The vehicle position recognition unit 11 may recognize theposition of the host vehicle on the map using a well-known method. Whenthe position of the host vehicle may be measured by a sensor disposedoutside the road and the like, the vehicle position recognition unit 11may recognize the position of the host vehicle by communicating with thesensor.

The obstacle recognition unit 12 recognizes obstacles (including thepositions of the obstacles) around the host vehicle based on thedetection result of the external sensor 2 and the map information of themap database 4. The obstacle recognition unit 12 detects the obstaclesusing the distance from the surface when the map information includesSurface Knowledge (surface data). The obstacle recognition unit 12 maydetect the obstacles using the distance from the surface by applying anestimated surface model to the detection result of the external sensor2. The obstacle recognition unit 12 may recognize the obstacles usingother well-known methods.

The obstacles include a stationary obstacle such as an electric powerpole, a guardrail, a tree, and a building that do not move, and a movingobstacle such as a pedestrian, a bicycle, and other vehicles. Forexample, the obstacle recognition unit 12 recognizes the obstacles eachtime the obstacle recognition unit 12 acquires the detection result fromthe external sensor 2.

The moving obstacle detection unit 13 detects a moving obstacle from theobstacles recognized by the obstacle recognition unit 12. The movingobstacle detection unit 13 detects the moving obstacle from theobstacles using Background Knowledge. The moving obstacle detection unit13 may detect the moving obstacle using other well-known methods.

The moving obstacle detection unit 13 estimates the movement amount ofthe moving obstacle at the time of detecting the moving obstacle. Themovement amount includes the movement direction and the movement speedof the moving obstacle. The movement amount may include the rotationalspeed of the moving obstacle. The moving obstacle detection unit 13 mayestimate an error in movement amount.

The moving obstacle detection unit 13 may specify the type of movingobstacle using information acquired by the external sensor 2. When themoving obstacle detection unit 13 specifies the type of moving obstacle,the moving obstacle detection unit 13 may correct the movement amountand the error in movement of the moving obstacle based on the type ofmoving obstacle.

The traveling state recognition unit 14 recognizes the traveling stateof the host vehicle based on the detection result of the internal sensor3 (for example, the vehicle speed information of the vehicle speedsensor, the acceleration information of the acceleration sensor, and theyaw rate information of the yaw rate sensor). For example, the travelingstate of the host vehicle includes the vehicle speed, the acceleration,and the yaw rate.

The first path generation unit 15 generates a first path of the hostvehicle by assuming all obstacles around the host vehicle to bestationary obstacles. The first path is a stationary obstacle avoidancepath that is generated using the method of assuming all obstacles to bestationary obstacles. The first path includes at least one candidatepath for causing the host vehicle to travel by avoiding the obstacles.Hereinafter, the assumption that all obstacles are stationary obstacleswill be referred to as a stationary obstacle assumption.

The first path generation unit 15 generates the first path based on thedetection result of the external sensor 2, the map information of themap database 4, the position of the host vehicle on the map recognizedby the vehicle position recognition unit 11, information of theobstacles recognized by the obstacle recognition unit 12, the travelingstate of the host vehicle recognized by the traveling state recognitionunit 14, and the like. The first path generation unit 15 may generatethe first path using other well-known methods.

The second path generation unit 16 generates a second path of the hostvehicle when a moving obstacle is assumed to move independently. Theindependent movement of the moving obstacle means that the movingobstacle moves independently of the presence of other obstacles and thehost vehicle. For example, it is assumed that another vehicle that isapproaching the host vehicle at a side of the host vehicle does notdecelerate for the presence of the host vehicle (does not interact) andmaintains its current direction and speed. Hereinafter, the assumptionthat the moving obstacle moves independently will be referred to as anindependent movement assumption.

The second path is an independent moving obstacle avoidance path that isgenerated using the method of the independent movement assumption. Thesecond path includes at least one candidate path for causing the hostvehicle to travel by avoiding the obstacles.

The second path generation unit 16 generates the second path using theindependent movement assumption based on the detection result of theexternal sensor 2, the map information of the map database 4, theposition of the host vehicle on the map recognized by the vehicleposition recognition unit 11, information of the obstacles recognized bythe obstacle recognition unit 12, the traveling state of the hostvehicle recognized by the traveling state recognition unit 14, and thelike.

Specifically, the second path generation unit 16 predicts a candidatepath of the moving obstacle using the independent movement assumption.When the moving obstacle is within a lane, the second path generationunit 16 can predict the candidate path on which the moving obstacletravels along the lane. When there is a branch point in the middle ofthe lane, the candidate path of the moving obstacle also branches intotwo or more. The second path generation unit 16 predicts a possiblecandidate path of the host vehicle using a well-known method. Thepossible candidate path of the host vehicle is a possible candidate pathof the host vehicle in which the influence of the presence of the movingobstacle is not considered. The candidate path that is included in thefirst path generated by the first path generation unit 15 may be used asthe possible candidate path of the host vehicle.

The second path generation unit 16 determines an overlap between thepossible candidate path of the moving obstacle and the possiblecandidate path of the host vehicle under the independent movementassumption. The second path generation unit 16 determines whether or notthe candidate path on which the moving obstacle moves independently ofthe presence of other obstacles and the host vehicle overlaps(intersects) with the possible candidate path of the host vehicle. Thesecond path generation unit 16 generates, as the candidate path of thesecond path, a candidate path that does not overlap the candidate pathof the moving obstacle on the independent movement assumption among thepossible candidate paths of the host vehicle.

When there is no candidate path of the host vehicle that does notoverlap the candidate path of the moving obstacle on the independentmovement assumption, the second path generation unit 16 performscalculation for avoiding collision by adjusting the vehicle speed (speedprofile) of the host vehicle. The second path generation unit 16generates, as the candidate path of the second path, a candidate path ofthe host vehicle on which collision can be avoided by adjusting thevehicle speed of the host vehicle. The second path generation unit 16may generate the second path using other well-known methods.

The second path generation unit 16 does not need to consider allobstacles (including the moving obstacle) in generation of the secondpath. The second path generation unit 16 may generate the second path byconsidering merely obstacles that have relatively significant influenceon generation of the path of the host vehicle. The second pathgeneration unit 16 can generate the second path by considering merelyobstacles positioned within a certain distance from the host vehiclebased on the point that obstacles positioned in the vicinity of the hostvehicle have relatively significant influence on generation of the pathof the host vehicle, and that obstacles positioned far from the hostvehicle have relatively insignificant (or no) influence on generation ofthe path of the host vehicle. Such a point also applies to generation ofa third path described below.

The third path generation unit 17 generates the third path of the hostvehicle when the moving obstacle is assumed to move while interactingwith at least one of the other obstacles or the host vehicle. Themovement of the moving obstacle while interacting with the otherobstacles and the host vehicle means that the moving obstacle moves withdeceleration and the like when needed in order to avoid a contact withanother obstacle or the host vehicle. The moving obstacle maytemporarily stop in order to avoid a contact with another obstacle orthe host vehicle. When the candidate path of the moving obstaclebranches into a plurality of paths, the candidate paths of the movingobstacle may be narrowed down using the detection result of the externalsensor 2. Hereinafter, the assumption that the moving obstacle moveswhile interacting with at least one of the other obstacles or the hostvehicle, or by narrowing down the paths of the moving obstacle will bereferred to as an interaction assumption.

The third path is an interacting moving obstacle avoidance path that isgenerated using the method of the interaction assumption. The third pathincludes at least one candidate path for causing the host vehicle totravel by avoiding the obstacles.

The third path generation unit 17 generates the third path using theinteraction assumption based on the detection result of the externalsensor 2, the map information of the map database 4, the position of thehost vehicle on the map recognized by the vehicle position recognitionunit 11, information of the obstacles recognized by the obstaclerecognition unit 12, the traveling state of the host vehicle recognizedby the traveling state recognition unit 14, and the like. The third pathgeneration unit 17 generates the third path by considering that themoving obstacle decelerates or temporarily stops due to interaction withat least one of the other obstacles or the host vehicle. In other words,the third path generation unit 17 generates more efficient path of thehost vehicle by considering the possibility of removing the influence ofthe moving obstacle. Generation of the third path using the interactionassumption will be described in detail below.

The reliability calculation unit 18 calculates the reliability of thesecond path and the reliability of the third path. The reliability ofthe second path is the result of evaluation of the appropriateness ofthe second path. The reliability of the third path is the result ofevaluation of the appropriateness of the third path. Calculation of thereliability of the second path and the reliability of the third pathwill be described in detail below.

The trajectory setting unit 19 sets a trajectory of the host vehicle fortraveling from the first path, the second path, and the third path basedon the reliability of the second path and the reliability of the thirdpath. When the reliability of the third path is higher than or equal toa third reliability threshold, the trajectory setting unit 19 sets thetrajectory of the host vehicle for traveling from the third path. Thethird reliability threshold is a threshold that is set in advance. Thetrajectory means a path that is finally used for traveling of the hostvehicle. The path is a candidate for the trajectory used for setting thetrajectory. When the third path includes one candidate path, thetrajectory setting unit 19 sets the candidate path as the trajectory ofthe host vehicle for traveling. For example, when there is a pluralityof candidate paths in the third path, the trajectory setting unit 19sets one candidate path as the trajectory of the host vehicle fortraveling from the viewpoint of traveling efficiency. The trajectorysetting unit 19 may set a candidate path having the shortest distance tothe destination as the trajectory of the host vehicle for traveling, ormay set a candidate path having the shortest time period before arrivalat the destination as the trajectory of the host vehicle for travelingby considering congestion and the like.

When the reliability of the third path is lower than the thirdreliability threshold, the trajectory setting unit 19 sets thetrajectory of the host vehicle for traveling from the second path whenthe reliability of the second path is higher than or equal to a secondreliability threshold. The second reliability threshold is a thresholdthat is set in advance. When the second path includes one candidatepath, the trajectory setting unit 19 sets the candidate path as thetrajectory of the host vehicle for traveling. When there is a pluralityof candidate paths in the second path, the trajectory setting unit 19sets one candidate path as the trajectory of the host vehicle fortraveling in the same manner as in the case of the third path.

When the reliability of the third path is lower than the thirdreliability threshold, and the reliability of the second path is lowerthan the second reliability threshold, the trajectory setting unit 19sets the trajectory of the host vehicle for traveling from the firstpath. When the first path includes one candidate path, the trajectorysetting unit 19 sets the candidate path as the trajectory of the hostvehicle for traveling. When there is a plurality of candidate paths inthe first path, the trajectory setting unit 19 sets one candidate pathas the trajectory of the host vehicle for traveling in the same manneras in the case of the third path.

The trajectory setting unit 19 constitutes the trajectory setting device101 according to the present embodiment. As illustrated in FIG. 1 , thevehicle position recognition unit 11, the obstacle recognition unit 12,the moving obstacle detection unit 13, the traveling state recognitionunit 14, the first path generation unit 15, the second path generationunit 16, the third path generation unit 17, the reliability calculationunit 18, and the trajectory setting unit 19 in the autonomous drivingsystem 100 constitute the trajectory setting device 101 that sets thetrajectory of the host vehicle.

The traveling plan generation unit 20 generates a traveling plan thatcorresponds to the trajectory set by the trajectory setting unit 19. Thetraveling plan generation unit 20 generates the traveling plancorresponding to the trajectory of the host vehicle based on at leastthe detection result of the external sensor 2 and the map information ofthe map database 4.

Although the traveling plan generation unit 20 is not limited inparticular, the traveling plan generation unit 20 preferably outputs thegenerated traveling plan, that is, the trajectory of the host vehicle,as a plurality of sets, each configured with two elements of a targetposition p and a speed v at each target point in a coordinate systemfixed with respect to the host vehicle. That is, each set isconfiguration coordinates (p,v). The target position p includes at leastthe positions of an x coordinate and a y coordinate or informationequivalent to the positions of the x coordinate and the y coordinate inthe coordinate system fixed with respect to the host vehicle. Thetraveling plan is not particularly limited, provided that the travelingplan describes the behavior of the host vehicle. For example, thetraveling plan may use target time t instead of the speed v, or thetarget time t and the azimuth of the host vehicle at the time may beadded to the traveling plan.

Generally, the traveling plan is simply data that represents a state inthe future after a few seconds from the current time. However, data thatindicates a state after a few tens of seconds is needed according tosituations such as a right turn at an intersection and overtaking of thehost vehicle. Thus, although it is not particularly limited, it ispreferable that the number of configuration coordinates of the travelingplan be changeable, and that the distance between the configurationcoordinates be changeable. A curve that connects the configurationcoordinates may be approximated using a spline function and the like,and parameters of the curve may be used as the traveling plan.Generation of the traveling plan can use any well-known method, providedthat the traveling plan can describe the behavior of the host vehicle.

The traveling plan may be data that indicates a change in the vehiclespeed, the acceleration/deceleration, the steering torque, and the likeof the host vehicle when the host vehicle travels the trajectory. Thetraveling plan may include a speed pattern, an acceleration/decelerationpattern, and a steering pattern of the host vehicle. The traveling plangeneration unit 20 may generate the traveling plan that has the shortesttrip time period (a needed time period that is needed for the hostvehicle to arrive at the destination).

For example, the speed pattern is data configured with a target vehiclespeed that is set in association with time per target control position.The target control positions are set on the trajectory at predeterminedintervals (for example, 1 m). For example, the acceleration/decelerationpattern is data configured with a target acceleration/deceleration thatis set in association with time per target control position. The targetcontrol positions are set on the trajectory at predetermined intervals(for example, 1 m). For example, the steering pattern is data configuredwith a target steering torque that is set in association with time pertarget control position. The target control positions are set on thetrajectory at predetermined intervals (for example, 1 m).

The traveling controller 21 automatically controls traveling of the hostvehicle based on the traveling plan generated by the traveling plangeneration unit 20. The traveling controller 21 outputs a control signalcorresponding to the traveling plan to the actuator 6. Accordingly, thetraveling controller 21 controls traveling of the host vehicle such thatthe host vehicle automatically travels in accordance with the travelingplan. The traveling controller 21 can execute autonomous driving of thehost vehicle using a well-known method.

Processes of Autonomous Driving System

Next, processes of the autonomous driving system 100 (processes of thetrajectory setting device 101) will be described. First, recognition ofthe autonomous driving system 100 will be described. It may be desirableto consider interaction with another vehicle in order to increase theaccuracy of recognition of the autonomous driving system 100. In otherwords, recognition and determination are associated with each other.Accordingly, the autonomous driving system 100 performs a plurality oftypes of determination (planning) according to the type of recognition.That is, the autonomous driving system 100 has several layers ofcalculation for determination (planning) according to the level ofrecognition. The layers correspond to the first path, the second path,and the third path.

Trajectory Setting Method

FIG. 2 is a flowchart illustrating a trajectory setting method in theautonomous driving system 100. The process of the flowchart illustratedin FIG. 2 is executed when needed during the autonomous driving control.

As illustrated in FIG. 2 , in S10, the ECU 10 of the autonomous drivingsystem 100 uses the first path generation unit 15 to generate the firstpath of the host vehicle (first path generation step). The first pathgeneration unit 15 generates the first path of the host vehicle when allobstacles around the host vehicle are assumed to be stationary obstacles(stationary obstacle assumption), based on the map information, theposition of the host vehicle on the map, information of the obstacles,and the traveling state and the like of the host vehicle.

In S12, the ECU 10 uses the trajectory setting unit 19 to set the firstpath as an output target.

In S14, the ECU 10 determines whether or not the moving obstacledetection unit 13 detects the moving obstacle from the obstacles (movingobstacle determination step). The moving obstacle detection unit 13detects the moving obstacle from the obstacles using BackgroundKnowledge. When the ECU 10 determines that the moving obstacle is notdetected from the obstacles (S14: NO), the ECU 10 transitions to S32.When the ECU 10 determines that the moving obstacle is detected from theobstacles (S14: YES), the ECU 10 transitions to S16.

In S16, the ECU 10 uses the second path generation unit 16 to generatethe second path of the host vehicle (second path generation step). Thesecond path generation unit 16 generates the second path when the movingobstacle is assumed to move independently (independent movementassumption), based on the map information, the position of the hostvehicle on the map, information of the obstacles, and the travelingstate and the like of the host vehicle.

In S18, the ECU 10 uses the reliability calculation unit 18 to calculatethe reliability of the second path (second path reliability calculationstep). Calculation of the reliability of the second path will bedescribed in detail below.

In S20, the ECU 10 uses the trajectory setting unit 19 to determinewhether or not the reliability of the second path is higher than orequal to the second reliability threshold. When the ECU 10 determinesthat the reliability of the second path is higher than or equal to thesecond reliability threshold (S20: YES), the ECU 10 transitions to S22.When the ECU 10 determines that the reliability of the second path islower than the second reliability threshold (S20: NO), the ECU 10transitions to S24.

In S22, the ECU 10 uses the trajectory setting unit 19 to overwrite theoutput target with the second path. That is, the output target ischanged to the second path from the first path. Then, the ECU 10transitions to S24.

In S24, the ECU 10 uses the third path generation unit 17 to generatethe third path of the host vehicle (third path generation step). Thethird path generation unit 17 generates the third path when the movingobstacle is assumed to move while interacting with at least one of theother obstacles or the host vehicle (interaction assumption), based onthe map information, the position of the host vehicle on the map,information of the obstacles, and the traveling state and the like ofthe host vehicle. Generation of the third path will be described indetail below.

In S26, the ECU 10 uses the reliability calculation unit 18 to calculatethe reliability of the third path (third path reliability calculationstep). Calculation of the reliability of the third path will bedescribed in detail below.

In S28, the ECU 10 uses the trajectory setting unit 19 to determinewhether or not the reliability of the third path is higher than or equalto the third reliability threshold. When the ECU 10 determines that thereliability of the third path is higher than or equal to the thirdreliability threshold (S28: YES), the ECU 10 transitions to S30. Whenthe ECU 10 determines that the reliability of the third path is lowerthan the third reliability threshold (S28: NO), the ECU 10 transitionsto S32.

In S30, the ECU 10 uses the trajectory setting unit 19 to overwrite theoutput target with the third path. That is, the output target is changedto the third path from the first path or the second path. Then, the ECU10 transitions to S32.

In S32, the ECU 10 uses the trajectory setting unit 19 to set thetrajectory of the host vehicle for traveling from the output target(trajectory setting step). When the output target is the first path, thetrajectory setting unit 19 sets one candidate path included in the firstpath as the trajectory of the host vehicle for traveling. When theoutput target is the second path, the trajectory setting unit 19 setsone candidate path included in the second path as the trajectory of thehost vehicle for traveling.

When the output target is the third path, the trajectory setting unit 19sets one candidate path included in the third path as the trajectory ofthe host vehicle for traveling. For example, when there is a pluralityof candidate paths, the trajectory setting unit 19 sets the candidatepath having the highest traveling efficiency as the trajectory of thehost vehicle for traveling. When the trajectory of the host vehicle fortraveling is set, the ECU 10 finishes the current process.

That is, determination (the first path, the second path, and the thirdpath) that corresponds to three types of recognition (the stationaryobstacle assumption, the independent movement assumption, and theinteraction assumption) is calculated. The ECU 10 may omit the processof S14 in the trajectory setting method. In such a case, the process ofS16 is started after the process of S12.

Third Path Generation Process

A third path generation process in the autonomous driving system 100will be described. FIG. 3 is a flowchart illustrating the third pathgeneration process. The third path generation process corresponds to theprocess of S26 in FIG. 2 .

As illustrated in FIG. 3 , in S40, the ECU 10 uses the third pathgeneration unit 17 to calculate the candidate path of the movingobstacle. The third path generation unit 17 calculates the candidatepath per moving obstacle (the possible candidate path of the movingobstacle) using the detection result of the moving obstacle detectionunit 13 and Traffic Rule Map.

In S42, the ECU 10 uses the third path generation unit 17 to acquire acandidate path matrix R of the host vehicle and the moving obstacle.First, determination/planning of autonomous driving (generation of thetraveling plan including trajectory setting) in the autonomous drivingsystem 100 will be described as a premise. Determination/planning ofautonomous driving is configured with two processes including dealingwith branching of a solution and calculating an appropriate trajectoryin selected branch points. The former will be referred to as intentiondecision, and the latter will be referred to as behavior decision.Considering that a branch point (unusual point) in a situation formed bya non-contact trajectory represents a risk, the intention decisionmainly deals with risk avoidance. In the intention decision, makingdetermination is prioritized. The behavior decision is calculation of atrajectory that can establish both of safety and efficiency within arange set by the intention decision. In the behavior decision, deferringdetermination is prioritized. Deferral of determination will bedescribed below.

The host vehicle and moving obstacles on a road network are denoted bya=1, 2, . . . , and possible candidate paths of a host vehicle a aredenoted by α=1, 2, . . . . A possible candidate path matrix of the hostvehicle a is denoted by R_(aα). It is considered that each vehiclecannot travel along with each other in a lane. Thus, considering anintention decision problem, a possible candidate path p_(aα) isconsidered to be a part (or a linked collection) of Trajectory andNavigation Definition File (RNDF) that is a line along the center of thelane. Accordingly, when the host vehicle a is at a point (any center ofthe lane) x_(a) on the road, a line that branches along the center ofthe road in front of the host vehicle a is a candidate path.

By assigning 1 to a case where the host vehicle a has a possibility oftaking the candidate path, and 0 to a case where the host vehicle a doesnot have a possibility of taking the candidate path, each element R_(aα)of the possible candidate path matrix of the host vehicle a can berepresented using General Formula (1).

$\begin{matrix}{R_{a\alpha} = \left\{ \begin{matrix}1 \\0\end{matrix} \right.} & (1)\end{matrix}$

The candidate path matrix R can be acquired not only for the hostvehicle a but also per moving obstacle.

In S44, the ECU 10 uses the third path generation unit 17 to acquire anoverlap matrix O that represents an overlap between the candidate paths.When the candidate path α of the host vehicle a and a candidate path βof a moving obstacle b are acquired, the two candidate paths α, β mayhave an overlap or may not have an overlap. When the candidate paths α,β do not have an overlap, the two moving obstacles do not have apossibility of colliding with each other. When the candidate paths α, βhave an overlap, the two moving obstacles have a possibility ofcolliding with each other. A symmetric matrix (overlap matrix) O_(aα,bβ)that represents the presence of an overlap can be acquired using GeneralFormula (2).

$\begin{matrix}{O_{{a\alpha},{b\beta}} = \left\{ \begin{matrix}1 & {{{When}{there}{is}{overlap}{between}{two}{candidate}{paths}a},b} \\0 & {Otherwise}\end{matrix} \right.} & (2)\end{matrix}$

While a set of the host vehicle and the moving obstacle is describedhere, the overlap matrix for the candidate paths can also be acquiredfor two moving obstacles. The same applies to various matrices describedbelow.

In S46, the ECU 10 uses the third path generation unit 17 to acquire acollision possibility matrix H. The collision possibility matrix H_(ab)of the host vehicle a and the moving obstacle b can be acquired usingGeneral Formula (3).

$\begin{matrix}{H_{ab} = {\sum\limits_{\alpha\beta}{R_{a\alpha}O_{{a\alpha},{b\beta}}R_{b\beta}}}} & (3)\end{matrix}$

It is considered that the possibility of collision can be zero when thehost vehicle a and the moving obstacle b can select the candidate pathR_(a) such that the collision possibility matrix H becomes a zero matrix(H=0). Since each moving obstacle selects a path toward its destination,the candidate path matrix R that establishes H=0 cannot be selected atall times. When the candidate path matrix R that establishes H=0 cannotbe selected, it is considered that each moving obstacle selects thecandidate path matrix R such that the number of non-zero elements in thecollision possibility matrix H is minimized. In such a case, the overlapbetween the candidate path α of the host vehicle a and the candidatepath β of the moving obstacle b is not resolved. Thus, the possibilityof collision may be determined by considering the movement speed of themoving obstacle, and collision may be avoided by temporally adjustingthe host vehicle a (adjusting the speed profile). In the adjustment ofthe speed profile, it is considered that the speed profile is adjustedfrom the viewpoint that “since it is mostly desired that the movingobstacle travel ahead of the host vehicle, collision is easily avoidedby allowing the moving obstacle to pass”.

In S48, the ECU 10 uses the third path generation unit 17 to acquire atiming matrix T. Determination of the possibility of collision in thepresence of an overlap between the candidate paths will be firstdescribed in a case where the overlap occurs at merely one point. Apoint where the candidate paths overlap each other is denoted byn_(aα,bβ). The length from x_(a) to n_(aα,bβ) measured along thecandidate path p_(aα) is denoted by l(n_(aα,bβ),x_(a)). When the movingbody is known, a time period t_(aα) needed for the host vehicle a toarrive at the point n_(aα,bβ) can be estimated using General Formula(4).

$\begin{matrix}{t_{a\alpha} = \frac{l\left( {n_{{a\alpha},{b\beta}},x_{a}} \right)}{V_{a}}} & (4)\end{matrix}$

Similarly, a time period t_(bβ) needed for the moving obstacle b toarrive at the point n_(aα,bβ) can be acquired. When the time periodsatisfies General Formula (5), the host vehicle a and the movingobstacle b come into contact with each other at the point n_(aα,bβ).When the time period satisfies General Formula (6), the host vehicle apasses through the point n_(aα,bβ) earlier than the moving obstacle b.t _(aα)=t _(b β). . .   (5)t _(aα)<t _(b β). . .   (6)

In such a case, the timing matrix T can be acquired as in GeneralFormula (7).

$\begin{matrix}{{T_{{a\alpha},{b\beta}}\left( n_{{a\alpha},{b\beta}} \right)} = \left\{ {\begin{matrix}{{sgn}\left( {t_{b\beta} - t_{a\alpha}} \right)} & , & {O_{{a\alpha},{b\beta}} = 1} \\0 & , & {O_{{a\alpha},{b\beta}} = 0}\end{matrix}.} \right.} & (7)\end{matrix}$

In S50, the ECU 10 uses the third path generation unit 17 to acquire aconflict tensor C. The timing matrix T represents which of the hostvehicle a and the moving obstacle b passes through the focused pointn_(aα,bβ) earlier. Thus, the timing matrix T satisfies General Formula(8).T(n_(aα, bβ))=−^(t)T(n_(aα, bβ))  . . . (8)

Considering that a predetermined difference δt in time is needed betweenthe time at which the host vehicle a passes through the point n_(aα,bβ),and the time at which the moving obstacle b passes through the pointn_(aα,bβ) in order for the host vehicle a and the moving obstacle b tosafely move, correction is performed as in General Formula (9). Then,the timing matrix T has an antisymmetric element and a symmetricelement.

$\begin{matrix}{{T_{{a\alpha},{b\beta}}\left( n_{{a\alpha},{b\beta}} \right)} = \left\{ \begin{matrix}{{sgn}\left( {t_{b\beta} - t_{a\alpha} - {\delta t}} \right)} & , & {O_{{a\alpha},{b\beta}} = 1} \\0 & , & {O_{{a\alpha},{b\beta}} = 0}\end{matrix} \right.} & (9)\end{matrix}$

In such a case, the conflict tensor (conflict matrix) C is acquiredusing General Formula (10).

$\begin{matrix}{{C\left( n_{{a\alpha},{b\beta}} \right)} = {\frac{1}{2}\left\{ {{T\left( n_{{a\alpha},{b\beta}} \right)} +^{t}{T\left( n_{{a\alpha},{b\beta}} \right)}} \right\}}} & (10)\end{matrix}$

A non-zero element of the conflict tensor C that is a symmetric matrixrepresents a set of a moving obstacle and a plan between which thedifference in time of passing through the point n_(aα,bβ) is smallerthan or equal to δt, that is, a set having a possibility of contact.

Next, the same can be applied to a case where the candidate pathsoverlap each other in a certain section. When two endpoints n^(n)_(aα,bβ), n^(l) _(aα,bβ) in the section having an overlap areconsidered, the possibility of contact is represented by satisfaction ofany of a first condition that the order of arrival of the host vehicle aand the moving obstacle b at one endpoint is different from the order atthe other endpoint, and a second condition that C(n_(aα,bβ)) is equal toone at any endpoint. The endpoint that is far from the host vehicle adoes not need to be a point where there is no overlap between thecandidate paths, and may be set as the position of the host vehicle aafter T seconds. The same applies to the moving obstacle b.

The first condition can be described as General Formula (11). Thus, anon-zero element of General Formula (12) represents the possibility ofcontact. In General Formula (12), “point” includes the endpoints of thesection, and [n^(n) _(aα,bβ),n^(f) _(aα,bβ)] represents a line segment.

$\begin{matrix}{{C_{{a\alpha},{b\beta}}\left( \left\lbrack {n_{{a\alpha},{b\beta}}^{n},n_{{a\alpha},{b\beta}}^{f}} \right\rbrack \right)} = {1 - {\frac{1}{2}{❘{{{sgn}\left( {t_{b\beta}^{n} - t_{a\alpha}^{n}} \right)} + {{sgn}\left( {t_{b\beta}^{f} - t_{a\alpha}^{f}} \right)}}❘}}}} & (11)\end{matrix}$ $\begin{matrix}{C_{{a\alpha},{b\beta}} = {{\sum\limits_{point}{C\left( n_{{a\alpha},{b\beta}} \right)}} + {\sum\limits_{line}{C\left( \left\lbrack {n_{{a\alpha},{b\beta}}^{n},n_{{a\alpha},{b\beta}}^{f}} \right\rbrack \right)}}}} & (12)\end{matrix}$

When information C_(aα,bβ) is acquired, the candidate path p_(aα) can beacquired from the map information. Consequently, quantities that shouldbe acquired by observation or estimation are merely the position x_(a)of the host vehicle or each moving obstacle and the speed v_(a) of thehost vehicle or each moving obstacle for a=1, 2, . . . . The differenceδt in time is set by a design parameter that is set for avoidingcollision. Other quantities are set by an estimation model ormeasurement by the sensor. While the speed v_(a) of the host vehicle maybe randomly assigned a different value per candidate path, the speed ofanother vehicle is assigned the measurement result or the value of theestimation model and thus, is not randomly assigned. Thus, thedependence of the host vehicle speed on the plan occurs for merely anelement of the conflict tensor C that is related to the host vehicle.This is represented as a numerical expression in General Formula (13).In General Formula (13), a denotes the host vehicle.C_(aα, bβ)=C_(a,α, bβ)(x_(a), v_(aα), x_(b), v_(b), δt)   . . . (13)

In S52, the ECU 10 uses the third path generation unit 17 to acquire aninterference matrix D. The interference matrix D is acquired usingGeneral Formula (14) as a matrix that is acquired by substituting theoverlap matrix O with the conflict tensor C from the viewpoint of anintention decision problem including collision avoidance by adjustingthe speed of the host vehicle a.

$\begin{matrix}{D_{ab} = {\sum\limits_{\alpha\beta}{R_{a\alpha}C_{{a\alpha},{b\beta}}R_{b\beta}}}} & (14)\end{matrix}$

The intention decision problem including collision avoidance byadjusting the speed of the host vehicle a can be considered to be aproblem that the host vehicle a and the moving obstacle b adjust theconflict tensor C by selecting the candidate path R_(aα) and the speedplan such that the interference matrix D represented by General Formula(14) becomes a zero matrix.

In S54, the ECU 10 uses the third path generation unit 17 to determinewhether or not the interference matrix D for the host vehicle is a zeromatrix. When the ECU 10 determines that the interference matrix D forthe host vehicle is a zero matrix (S54: YES), the ECU 10 transitions toS68. When the ECU 10 determines that the interference matrix D for thehost vehicle is not a zero matrix (S54: NO), the ECU 10 transitions toS56.

In S56, the ECU 10 uses the third path generation unit 17 to narrow downthe candidate paths of the host vehicle. The third path generation unit17 narrows down the candidate paths of the host vehicle by assuming thateach moving obstacle follows a traffic rule that is set in advance. Thetraffic rule is stored in association with the position information onthe map in Traffic Rule Map of the map database 4.

In the intention decision problem, it may not be appropriate to considerall possible behaviors of another moving obstacle. For example,considering the possibility that all oncoming vehicles on a roadconfigured with two lanes of a traveling lane of the host vehicle and anopposing lane depart from their lane and appear in front of the hostvehicle, the host vehicle may have to be stopped until there is nooncoming vehicle. Since the driver usually does not stop the hostvehicle until there is no oncoming vehicle, an assumption is consideredthat driving performed by the driver in the actual environment isdetermined based on certain social compact (social expectation).Hereinafter, such a point will be separately considered at the intentiondecision level related to the candidate path matrix R_(a) and thebehavior decision level related to the conflict tensor C.

First, an assumption referred to as “path overlap avoidance assumption”will be illustrated as an intention decision principle. The value of anelement of the interference matrix may be equal to 1 (there is apossibility of collision) when the paths of the host vehicle and themoving obstacle (or two moving obstacles) overlap each other. That is,the possibility of collision may be minimized when all moving obstaclesselect a plan that does not overlap the paths of another moving obstacleand the host vehicle. It is considered that for each moving obstacle,reasonable selection of a plan is selecting a plan that does not overlapthe paths of another moving obstacle and the host vehicle, andmaintaining the selected plan provided that the plan does not impede themovement of the moving obstacle toward the destination. Such selectionof a plan by each moving obstacle will be referred to as “path overlapavoidance assumption”.

When several types of the path overlap avoidance assumption arespecifically described, a first assumption is that a plan such astraveling in the opposing lane that does not follow the traffic rule isnot selected. A second assumption is that a plan that accompanies lanechanges that are not needed is not selected. A third assumption is thatwhen the destination of the moving obstacle is not known, the samenumber of plans as branches are considered at branches of a trajectorysuch as an intersection. For example, when the moving obstacle isanother vehicle, it is considered that the destination of the movingobstacle is acquired by vehicle-to-vehicle communication and the like.The third path generation unit 17 narrows down the candidate paths ofthe host vehicle using a well-known method with the path overlapavoidance assumption.

In S58, the ECU 10 uses the third path generation unit 17 to acquire theinterference matrix D again. In S60, the ECU 10 uses the third pathgeneration unit 17 to determine again whether or not the interferencematrix D for the host vehicle is a zero matrix. When the ECU 10determines that the interference matrix D for the host vehicle is a zeromatrix (S60: YES), the ECU 10 transitions to S68. When the ECU 10determines that the interference matrix D for the host vehicle is not azero matrix (S60: NO), the ECU 10 transitions to S62.

In S62, the ECU 10 uses the third path generation unit 17 to calculatethe vehicle speed (speed profile) of the host vehicle for each non-zeroelement of the interference matrix using an altruistic strategy suchthat the non-zero element becomes zero. The altruistic strategy isillustrated as an order decision principle for causing the conflicttensor to become a zero matrix. When the element C_(aα,bβ) of theconflict tensor is not zero, there is a possibility (possibility ofcontact) that the absolute value of the difference between the time ofarrival of the host vehicle a at a point of a path overlap and the timeof arrival of the moving obstacle b at the point is smaller than orequal to δt. A condition for avoiding contact of the host vehicle a canbe represented using General Formula (15).|t_(aα)−t_(bβ)|>δt   . . . (15)

In such a case, General Formula (16) and General Formula (17) can beacquired using General Formula (4).

$\begin{matrix}{{\frac{1\left( {n_{{a\alpha},{b\beta^{\prime}}}x_{a}} \right)}{v_{a}} - t_{b\beta}} > {\delta t}} & (16)\end{matrix}$ $\begin{matrix}{{{- \frac{1\left( {n_{{a\alpha},{b\beta^{\prime}}}x_{a}} \right)}{v_{a}}} + t_{b\beta}} > {\delta t}} & (17)\end{matrix}$

A condition for allowing the moving obstacle b to pass can be describedas General Formula (18) from General Formula (16) and General Formula(17). A condition for causing the host vehicle a to go first can bedescribed as General Formula (19).

$\begin{matrix}{v_{a} < \frac{1\left( {n_{{a\alpha},{b\beta^{\prime}}}x_{a}} \right)}{t_{b\beta} + {\delta t}}} & (18)\end{matrix}$ $\begin{matrix}{\frac{1\left( {n_{{a\alpha},{b\beta^{\prime}}}x_{a}} \right)}{t_{b\beta} - {\delta t}} < v_{a}} & (19)\end{matrix}$

When collision is avoided by allowing the moving obstacle to pass thehost vehicle, it is considered that the speed of the host vehicle isadjusted to satisfy General Formula (18). Avoidance of collision byallowing the moving obstacle to pass the host vehicle will be referredto as conflict resolution using altruistic strategy. When the hostvehicle and merely one moving obstacle are present in the range ofinteraction, a stable traffic situation as a whole can be made bycausing the host vehicle to pass ahead of the moving obstacle even whenthe moving obstacle is traveling at a speed above a speed limit. Thesame applies to a case where the moving obstacle passes ahead of thehost vehicle. Thus, such an altruistic strategy is considered as asuggestion.

In S64, the ECU 10 uses the third path generation unit 17 to determinewhether or not the host vehicle can have a vehicle speed (speed profile)at which the interference matrix D becomes a zero matrix. When the ECU10 determines that the host vehicle cannot have a vehicle speed at whichthe interference matrix D becomes a zero matrix (S64: NO), the ECU 10transitions to S66. When the ECU 10 determines that the host vehicle canhave a vehicle speed at which the interference matrix D becomes a zeromatrix (S64: YES), the ECU 10 transitions to S68.

In S66, the ECU 10 uses the HMI 5 to request the driver to intervene.The ECU 10 notifies the driver of a request for takeover (switching tomanual driving from autonomous driving) by transmitting a control signalto the HMI 5.

When the driver is requested to intervene, it is considered that thereare two or more moving obstacles in the range of interaction of the hostvehicle. In such a case, even when the host vehicle a and the movingobstacle b are in a consistent state, the host vehicle a may want togive way to a third moving obstacle c, but the moving obstacle c maywant to go first. In such a case, it is difficult for the movingobstacle c to set its state within the range of the altruistic strategy.Specifically, one example of such a scene is when the host vehicle aenters a priority road from a non-priority road while the other vehicleb that interferes with the host vehicle a is present in the priorityroad, and the other vehicle c having a low speed is present behind thehost vehicle a. In such a case, opposition between intentions cannot beresolved by the altruistic strategy such that the host vehicle a givesway, and as a suggestion, it should be considered that the other vehiclec behind the host vehicle a is also expected to decelerate (correct theplan or reverse its intention to go first to an intention to give way)in order to observe the traffic rule and resolve the opposition betweenintentions.

A more complex case is an unstable state known as frustration instatistical physics. Such a state is when reversing the intention of themoving obstacle b needs reversing the intention of the host vehicle a inthe above case. In such a case, a strategy of making any settlement suchas reducing the interaction between the host vehicle a and the movingobstacles b, c is considered. In the case of autonomous driving, onemethod of reducing the interaction is increasing the effective distancebetween vehicles by decreasing the speed of the host vehicle a.

When there are two moving obstacles in addition to the host vehiclewithin the range of interaction, a dilemma may be present such thatconflict as a whole cannot be surely resolved by merely the hostvehicle. In such a case, it is considered that the driver is requestedto intervene. When the host vehicle a is in a dilemma with the othermoving obstacles b, c, General Formula (20) is established for any(α,v_(aα)). Thus, the dilemma can be detected from the conflict tensorC.

$\begin{matrix}{\left\{ {{{\sum\limits_{\beta}C_{{a\alpha},{b\beta}}} = 0},{{\sum\limits_{\gamma}C_{{a\alpha},{c\gamma}}} \neq 0}} \right\}{OR}\left\{ {{{\sum\limits_{\beta}C_{{a\alpha},{b\beta}}} \neq 0},{{\sum\limits_{\gamma}C_{{a\alpha},{c\gamma}}} = 0}} \right\}} & (20)\end{matrix}$

In S68, the ECU 10 uses the third path generation unit 17 to generatethe remaining candidate path as the third path of the host vehicle.Then, the ECU 10 finishes the current process.

While the third path generation process is described thus far, the sameparts as in the second path generation process may be employed in thesecond path generation process.

Entrance into Roundabout

An entrance of the host vehicle into a roundabout will be illustratedwith respect to the third path generation process. The candidate path ofthe host vehicle α=1 includes a candidate path α=1 that enters aroundabout, and a candidate path α=2 that waits in front of theroundabout. When the other vehicle b (moving obstacle b) is traveling inthe roundabout, the candidate path β of the other vehicle b includes acandidate path β=1 that exits from the roundabout, and a candidate pathβ=2 that remains in the roundabout.

There is an overlap between the candidate path α=1 of the host vehicle aand merely the candidate path β=2 of the other vehicle b that remains inthe roundabout. The overlap matrix O can be described as General Formula(21) and General Formula (22).

$\begin{matrix}{O_{{1\alpha},{2\beta}} = \begin{pmatrix}O_{11,21} & O_{11,22} \\O_{12,21} & O_{12,22}\end{pmatrix}_{\alpha\beta}} & (21)\end{matrix}$ $\begin{matrix}{O_{{1\alpha},{2\beta}} = \begin{pmatrix}0 & 1 \\0 & 0\end{pmatrix}_{\alpha\beta}} & (22)\end{matrix}$

The timing matrix T can be described as General Formula (23). The termτ₁₂ in General Formula (23) is represented as General Formula (24), andthe term τ₂₁ in General Formula (23) is represented as General Formula(25). The subscript outside the parentheses is a representation that isintroduced for convenience in order to clearly show the parameter in theparentheses.

$\begin{matrix}{T_{{a\alpha},{b\beta}} = \begin{pmatrix}\begin{pmatrix}0 & 0 \\0 & 0\end{pmatrix}_{\alpha\beta} & \begin{pmatrix}0 & \tau_{12} \\0 & 0\end{pmatrix}_{\alpha\beta} \\\begin{pmatrix}0 & 0 \\\tau_{21} & 0\end{pmatrix}_{\alpha\beta} & \begin{pmatrix}0 & 0 \\0 & 0\end{pmatrix}_{\alpha\beta}\end{pmatrix}_{ab}} & (23)\end{matrix}$ $\begin{matrix}{\tau_{12} = {{sgn}\left( {t_{22} - t_{11} - {\delta t}} \right)}} & (24)\end{matrix}$ $\begin{matrix}{\tau_{21} = {{sgn}\left( {t_{11} - t_{22} - {\delta t}} \right)}} & (25)\end{matrix}$

A case where the candidate paths employed by the other vehicle b are notnarrowed down, and the host vehicle a is assumed to enter the roundaboutwill be illustrated below. First, the fact that the candidate paths ofthe other vehicle b are not narrowed down is represented by GeneralFormula (26). The entrance of the host vehicle a into the roundabout isrepresented by General Formula (27).R_(2β)=(1 1)β  . . . (26)R_(1α)=(1 0)_(α)  . . . (27)

In such a case, the interference matrix D is represented in GeneralFormula (28) to General Formula (30).

$\begin{matrix}{D_{ab} = {\sum\limits_{\alpha\beta}{R_{a\alpha}C_{{a\alpha},{b\beta}}R_{b\beta}}}} & (28)\end{matrix}$ $\begin{matrix}{= {\sum\limits_{\alpha\beta}{\left( {1,0} \right)_{\alpha}{C_{{a\alpha},{b\beta}}\left( {1,1} \right)}_{\beta}}}} & (29)\end{matrix}$ $\begin{matrix}{= \begin{pmatrix}0 & {\frac{1}{2}\left( {\tau_{12} + \tau_{21}} \right)} \\{\frac{1}{2}\left( {\tau_{12} + \tau_{21}} \right)} & 0\end{pmatrix}_{ab}} & (30)\end{matrix}$

In order to avoid contact between the host vehicle a and the othervehicle b, the speed profile of the host vehicle a should be adjustedsuch that the host vehicle α=1 has τ₁₂=0 in order for the interferencematrix D to become a zero matrix.

When all of the cases where the interference matrix D becomes a zeromatrix in the passage through the roundabout are exemplified using therepresentations thus far, there are three cases (A) the host vehicle atakes the candidate path R_(1α)=(0,1)_(α) that does not enter theroundabout, (B) the host vehicle a enters the roundabout, and the othervehicle b=2 is estimated to employ the candidate path R_(2β)=(1,0)_(β),and (C) the host vehicle a enters the roundabout, and the speed profileof the host vehicle a is adjusted to establish c=0.

In the case (B), the interference matrix D is represented by GeneralFormula (31) to General Formula (33), and the possibility of contact isequal to zero. Thus, the host vehicle a can immediately enter theroundabout.

$\begin{matrix}{D_{ab} = {\sum\limits_{\alpha\beta}{R_{1\alpha}C_{{a\alpha},{b\beta}}R_{2\beta}}}} & (31)\end{matrix}$ $\begin{matrix}{= {\sum\limits_{\alpha\beta}{\left( {1,0} \right)_{\alpha}{C_{{a\alpha},{b\beta}}\left( {1,1} \right)}_{\beta}}}} & (32)\end{matrix}$ $\begin{matrix}{= \begin{pmatrix}0 & 0 \\0 & 0\end{pmatrix}_{ab}} & (33)\end{matrix}$

The candidate path β employed by the other vehicle b=2 in (B) thatcorresponds to a branch of the path in (C) is estimated before the speedprofile is calculated in the case (C). Consequently, a function thatmakes an immediate entrance into the roundabout when the other vehicle bexits from the roundabout can be realized. A direction h_(b) of theother vehicle (moving obstacle) b may be additionally introduced.

Time Shift Process

A time shift process will be described. The sensor of the autonomousdriving system 100 measures the outside-vehicle environment.Consequently, a time delay Δt occurs until the actuator 6 starts tooperate. Considering that the host vehicle starts to move after Δt fromthe time of measurement by the sensor, planning of the host vehicle isperformed in a space where predictive correction corresponding to thetime period Δt is made by shifting the position of the moving bodyoutside the vehicle and the position x_(a) of the host vehicle tox_(a)+v_(a)Δt.

Deferral of Determination

Deferral of determination will be described. When the scope of searchingfor the candidate path is D={p(τ)}, the candidate path can be defined asin General Formula (34) and General Formula (35) from the viewpoint ofsafety and traveling efficiency. In such a case, the state representedin General Formula (36) is achieved.Safety-prioritized candidate path {p^(s)(τ)}=

{S(p(τ), E (s))|D}  . . . (34)Efficiency-prioritized candidate path {p

(τ)}=

{E(p(r), E (s))|D}  . . . (35)}p^(s)(τ)}∩{p

(τ)}  . . . (36)

A safety evaluation function is denoted by S(p(τ),E(s)), and a travelingefficiency evaluation function is denoted by E(p(τ),E(s)).

A smooth candidate path can be acquired by “switching to a candidatepath prioritizing safety at time t+δt even when a candidate pathprioritizing traveling efficiency is selected as the candidate path attime t”.

A situation where a pedestrian is present in a roadside will bedescribed as a specific example. In such a case, determination can bedeferred as follows. (A) When strong braking is applied, the hostvehicle can have sufficient time to stop even when the pedestrian entersthe trajectory of the host vehicle for traveling. (B) When the hostvehicle has sufficient time to stop, the host vehicle temporarilytravels by prioritizing efficiency considering that “the pedestrian maynot enter the trajectory of the host vehicle for traveling”. (C) Whenthe pedestrian disappears, the host vehicle maintains its traveling. (D)When there is still a possibility that “the pedestrian enters thetrajectory of the host vehicle for traveling”, a return is made to thedetermination (A).

Specifically, first, a final stop position with respect to thepedestrian is set. Next, a strong braking start position from which thehost vehicle can stop at the final stop position using “strong braking”is acquired. A plan that prioritizes efficiency is employed to thestrong braking start position from the current position (for example,the current speed is maintained).

Calculation of Reliability

Calculation of the reliability of the second path and the reliability ofthe third path by the reliability calculation unit 18 will be described.Reliability broadly includes the reliability of sensing of the hostvehicle and the reliability of the result of signal processing that isperformed based on the sensing result.

Reliability of Sensing of Host Vehicle

The reliability of sensing of the host vehicle is reliability calculatedas the degree to which the external sensor 2 of the host vehicle detectsthe outside-vehicle environment, using “the known appearance of theoutside-vehicle environment that is acquired using the external sensor 2of the host vehicle”. In the present embodiment, the reliability ofsensing of the host vehicle means the reliability of sensing ofautonomous driving.

The reliability calculation unit 18 calculates the reliability ofsensing of autonomous driving by comparing the map information of themap database 4 with the detection result of the external sensor 2. Whena prior-knowledge/map M(s,x) that is set as coordinates is used forrecognition, it is considered that General Formula (37) that combines asignal s(t) of the external sensor 2 with the prior-knowledge/map M(s,x)is introduced.{circumflex over (x)}(t)=arf_(min){d(s(t), s(x))}  . . . (37)

A sensor signal that is expected to be acquired at the position xacquired from the prior-knowledge/map M(s,x) is denoted by s(x).Although it is not limited in particular, the position x preferablyincludes an azimuth h of the host vehicle when needed. The distancebetween sensor signals is denoted by d(.,.).

After the outside-vehicle environment is sensed, the host vehicleposition is estimated (localized) in the autonomous driving system 100.The host vehicle position is estimated by the vehicle positionrecognition unit 11 comparing the detection result of the externalsensor 2 with internal Localization Knowledge. In order to estimate thehost vehicle position, the feature point stored in LocalizationKnowledge needs to be detected by the external sensor 2. The reliabilitycalculation unit 18 calculates the reliability of sensing of autonomousdriving using the ratio of detected feature points, a difference Δs(t,x)in sensing signal represented in General Formula (38), and the like.Δs(t, x)=s(t)−s({circumflex over (x)}(t))   . . . (38)

The autonomous driving system 100 can evaluate the reliability ofsensing of autonomous driving (acquired from the external sensor 2 orLocalization Knowledge) by regarding the difference between thedetection result in a structure recognition layer (the result ofrecognizing the structure of the outer world, that is, theoutside-vehicle environment) and the prior-knowledge (structurerecognition error) as abnormality. While the structure recognition errorcan be defined in various manners, it is considered that the structurerecognition error is simply represented by General Formula (39) andGeneral Formula (40) when a designed threshold is set asΔε_(i)(t)=|ε_(l)({circumflex over (x)})|, Δε.

$\begin{matrix}{{\Delta{S^{2}(t)}} = {\sum\limits_{i = 1}^{N}{\frac{1}{2N}\Delta{\varepsilon_{i}(t)}^{2}{\theta\left( {\theta_{\varepsilon} - {\Delta{\varepsilon_{i}(t)}}} \right)}}}} & (39)\end{matrix}$ $\begin{matrix}{{N_{s}(t)} = {\sum\limits_{i = 1}^{N}\left( {1 - {\theta\left( {\theta_{\varepsilon} - {\Delta{\varepsilon_{i}(t)}}} \right)}} \right.}} & (40)\end{matrix}$

The cumulative value of distance errors in reflection points having anerror less than or equal to θ_(E) is denoted by ΔS²(t). The number ofreflection points where the error exceeds θ_(E) is denoted by N_(s)(t).Both of ΔS²(t) and N_(s)(t) become zero when all feature points storedin Localization Knowledge completely match the feature points in thesensor signal. As the distance error is increased, that is, as thematching feature points are decreased, the values of ΔS²(t) and N_(s)(t)are increased. The two quantities can be combined to introduce aquantity of the estimated structure recognition error. The same can beapplied to Traffic Light Location. Both of ΔS²(t) and N_(s)(t) arepositioned in a self-monitoring function that uses the structurerecognition layer.

The reliability of sensing of the host vehicle (the reliability ofsensing of autonomous driving) described thus far is used in bothcalculation of the reliability of the second path and calculation of thereliability of the third path. For example, the reliability calculationunit 18 calculates the reliability of the second path and thereliability of the third path as a lower value as the reliability ofsensing of the host vehicle is decreased.

Reliability of Result of Signal Processing Performed Based on SensingResult

The autonomous driving system 100 is configured to not only performtracking but also perform several estimations or predictions for themoving obstacle. Specifically, three estimations or predictionsincluding estimation of the intention of the moving obstacle b seen fromthe host vehicle a and dynamic prediction and symbolic prediction of themoving obstacle b are considered.

The two predictions of the symbolic prediction and the dynamicprediction that are related to prediction of quantities such as theposition of the moving obstacle describing the motion of the movingobstacle are classified for the reliability of prediction of thecandidate path of the moving obstacle in the independent movementassumption. Hereinafter, prediction of the candidate path of the movingobstacle in the independent movement assumption will be referred to asindependent moving obstacle prediction.

The intention estimation prediction that predicts the trajectory themoving obstacle will take is classified for the reliability ofprediction of the candidate path of the moving obstacle in theinteraction assumption. Hereinafter, prediction of the candidate path ofthe moving obstacle in the interaction assumption will be referred to asinteractive moving obstacle prediction.

Reliability of Independent Moving Obstacle Prediction

The reliability of the independent moving obstacle prediction affectsthe reliability of the second path. In the estimation of the intentionof the moving obstacle b seen from the host vehicle a, calculation ofthe reliability and self-monitoring can be performed using thereliability of the estimation result. In prediction of Xa of the movingobstacle b seen from the host vehicle a, calculation of the reliabilityand self-monitoring can be performed using a prediction error δX_(ab)(t)represented in General Formula (41). An operator for predicting a statein the future after δt is denoted by {circumflex over (T)}(δt).δX_(ab)(t)=X_(ab)(t)−{circumflex over (T)}(δt)X_(ab)(t−δt)   . . . (41)

More specifically, in calculation of the reliability and self-monitoringusing the reliability, it is considered that the following quantitiesare used for each estimation or prediction. The symbolic prediction isprediction based on the result of recognizing whether each movingobstacle is a vehicle or a pedestrian. Thus, high prediction accuracy insuch a layer means a state where “motions around the host vehicle arewell seen”. Basically, macro estimated quantities (the position x, theazimuth h, and the speed v) of the moving obstacle can be estimatedunder a model constraint condition M that targets “vehicle” or the like,that is, estimated by {circumflex over (T)}(δt, M, x, h, v) and theprediction error δX_(ab)(t) can be calculated.

The dynamic prediction is the most basic prediction and is considerednot to be associated with the recognition level of a person such as“well reading”. The macro estimated quantities (the position x, theazimuth h, and the speed v) of the moving obstacle can be calculatedusing a Kalman filter and a particle filter, that is, estimated by{circumflex over (T)}(δt, x, h, v), and the prediction error δX_(ab)(t)and likelihood can be calculated. The level of reliability of each ofthe symbolic prediction and the dynamic prediction is preferablyevaluated, for example, using the magnitudes of the error and thelikelihood.

For example, the reliability calculation unit 18 can calculate thereliability of the independent moving obstacle prediction based on thelikelihood of the particle filter that predicts a change in thedistribution of reflection points which are determined as reflectionpoints from the moving obstacle by LIDAR. The reliability calculationunit 18 may use the likelihood of the particle filter as the reliabilityof the independent moving obstacle prediction. Alternatively, thereliability of the independent moving obstacle prediction may becalculated using a method that uses the error covariance matrix of theKalman filter.

The reliability calculation unit 18 calculates the reliability of thesecond path (independent moving obstacle avoidance path) based on thereliability of the independent moving obstacle prediction and thereliability of sensing of the host vehicle. For example, the reliabilitycalculation unit 18 calculates the reliability of the second path as ahigher value as the reliability of the independent moving obstacleprediction is increased.

When prediction is performed using a model, the reliability of the modelmay be evaluated using the likelihood or a statistical quantity similarto the likelihood acquired at the identification of the moving obstacle.By using the variance of prediction of the future position acquired atthe prediction of dynamic time evolution using the model, thereliability of the independent moving obstacle prediction may bedecreased as the variance is increased.

Reliability of Interactive Moving Obstacle Prediction

The reliability of the interactive moving obstacle prediction affectsthe reliability of the third path. For example, interaction in theautonomous driving system 100 can be regarded as a change in behaviorfor avoiding collision between vehicles. More strictly, interaction is achange in behavior for reducing the possibility of collision betweenvehicles as much as possible. Generally, when the future behavior of thevehicle can be accurately estimated (when the reliability of predictionis high), the possibility of collision between vehicles can be easilydecreased.

When the future behavior of the vehicle is not sufficiently known, it isconsidered that the reduction of the possibility of collision betweenvehicles is limited. A change in behavior for avoiding collision betweenvehicles in a traffic environment cannot be described by merely aphysical law but by considering a model that describes the behavior ofthe moving body under an environment including the structure of the roadand the traffic rule. Thus, a method of calculating the reliabilityneeds to be based on the model. “Entrance into Roundabout” describedabove will be used as the model describing a change in behavior foravoiding collision between vehicles in a traffic environment.

The reliability of the interactive moving obstacle prediction iscalculated in estimation where the interference matrix D_(ab) is beingacquired. Specifically, such estimation includes estimation of thepositions of the host vehicle a and the moving obstacle b forcalculating the conflict tensor C, estimation of the speed, andestimation of the candidate path matrix R by narrowing down the paths.

The conflict tensor C is represented in General Formula (42). The hostvehicle is denoted by a.C_(aα, bβ)=C_(aα, bβ)(x_(a), v_(aα), x_(b), δt)   . . . (42)

The speed v_(b) of the other vehicle b is a measured quantity. When aplurality of measurements is performed, a variance δv_(b) of the speedv_(b) can be calculated. For each possible candidate path β of the othervehicle b, a time period t_(bβ) for reaching a point where the candidatepath β overlaps the candidate path of the host vehicle a is representedin General Formula (43) and General Formula (44).

$\begin{matrix}{{t_{b\beta} + {\delta t_{b\beta}}} = \frac{1\left( {n_{{a\alpha},{b\beta}},x_{ab}} \right)}{v_{b} + {\delta v_{b}}}} & (43)\end{matrix}$ $\begin{matrix}{\sim {t_{b\beta} - {\frac{1\left( {n_{{a\alpha},{b\beta}},x_{ab}} \right)}{v_{b}}\delta v_{b}}}} & (44)\end{matrix}$

Thus, a variance l(n_(aα,bβ),x_(b))σ_(vb)/v_(b) of the time periodt_(bβ) is acquired. A distribution ρ(t) of the difference in timebetween the host vehicle a that passes through the position n_(aα,bβ)first, and the other vehicle b that passes through the positionn_(aα,bβ) is a distribution of the variance having its center at(t_(bβ)−t_(aα)).

A probability P_(aα,bβ) that the difference in time of passing throughthe position n_(aα,bβ) between the host vehicle a and the other vehicleb is less than or equal to δt is represented in General Formula (45).

$\begin{matrix}{P_{{a\alpha},{b\beta}} = {\int_{- \infty}^{\delta t}{{\rho(t)}{dt}}}} & (45)\end{matrix}$

The possibility of contact can be estimated as in General Formula (46)by comparing the probability with a threshold θ_(c).

$\begin{matrix}{C_{{a\alpha},{b\beta}} = \left\{ \begin{matrix}0 & {P_{{a\alpha},{b\beta}} \leq \theta_{c}} \\1 & {otherwise}\end{matrix} \right.} & (46)\end{matrix}$

One of preferable indexes indicating the reliability of estimation ofthe possibility of contact is Index (47) that is the ratio of thethreshold θ_(c) to the probability

$\begin{matrix}\frac{\theta_{c}}{P_{{a\alpha},{b\beta}}} & (47)\end{matrix}$

When the speed of the other vehicle b is not measured, it is consideredthat v_(b) is substituted with a legal speed (a legal speedcorresponding to the position of the host vehicle a on the map). In sucha case, the reliability of C_(aα,bβ) is preferably substituted, forexample, with low reliability that is set in advance. The reliability ofC_(aα,bβ) is one example of the reliability of the interactive movingobstacle prediction. Alternatively, an offset quantity from a separationplane in a support vector machine is considered as one example.

The reliability calculation unit 18 calculates the reliability of thethird path (interactive moving obstacle avoidance path) based on thereliability of the interactive moving obstacle prediction and thereliability of sensing of the host vehicle. For example, the reliabilitycalculation unit 18 calculates the reliability of the third path as ahigher value as the reliability of the interactive moving obstacleprediction is increased.

Reliability of Candidate Path Matrix

Information that is needed for acquiring the candidate path matrix usingthe path overlap avoidance assumption is merely the position of themoving obstacle. When the candidate path includes a branch point of thepath such as an intersection, a plurality of candidate paths is assigned1 in the candidate path matrix that is acquired using the path overlapavoidance assumption. One example is the discussion about theroundabout. The candidate path matrix R can be narrowed down as inGeneral Formula (48).R_(2β)=(1 1)β→R_(2β=()1 0)β  . . . (48)

That is, the candidate path matrix having two possibilities fromestimation based on the path overlap avoidance assumption is narroweddown to a candidate path matrix having one possibility by observing themoving obstacle in detail. By narrowing down the candidate path, theautonomous driving vehicle can travel efficiently.

The candidate path matrix has a relationship in General Formula (49)from its definition.

$\begin{matrix}{{\sum\limits_{\beta}R_{b\beta}} \geq 1} & (49)\end{matrix}$

As the value of the relationship is decreased, the intention (selectedpath) of the moving obstacle b is well read.

In the actual environment, interaction between the moving obstacle b andthe host vehicle a needs to be considered near the branch point in orderto read the intention of the moving obstacle b about selecting acandidate path branching off from the branch point. A probabilityp(a,b,β) of the moving obstacle b selecting the candidate path β needsnot only macro measured values of the moving obstacle b but also macromeasured values of the host vehicle a. The macro measured values arerepresentatively a distance d to the branch point from the position ofthe moving obstacle b, the speed v of the moving obstacle b, and thedirection h of the vehicle body of the moving obstacle b. That is, theprobability p(a,b,β) of the moving obstacle b selecting the path β seenfrom the host vehicle a is represented in General Formula (50).ρ(a, b, β)=ρ(a, b, β:d_(a), h_(a), d_(b), v_(b), h_(b))   . . . (50)

The probability function can be more accurately reproduced when asufficient amount of data near the branch point is provided. A processrepresented in General Formula (51) is performed by acquiring theprobability function and comparing the probability function with thethreshold θ.

$\begin{matrix}{R_{b\beta} = \left\{ \begin{matrix}0 & {{\rho\left( {a,b,{\beta:d_{a}},v_{a},h_{a},d_{b},v_{b},h_{b}} \right)} \leq \theta} \\1 & {otherwise}\end{matrix} \right.} & (51)\end{matrix}$

By performing such a process, the intention (selected path) of themoving obstacle b seen from the host vehicle a can be narrowed down.General Formula (52) that is the ratio of the threshold θ to theprobability ρ(a,b,β: d_(a),v_(a),h_(a),d_(b),v_(b),h_(b)) is onepreferable example of the narrowed reliability.

$\begin{matrix}\frac{\theta}{\rho\left( {a,b,{\beta:d_{a}},v_{a},h_{a},d_{b},v_{b},h_{b}} \right)} & (52)\end{matrix}$

Such a function can be realized using a support vector machine or thelike when data including the distance d to the branch point from theposition of the moving obstacle b, the speed v of the moving obstacle b,and the direction h of the vehicle body of the moving obstacle b isprovided. When a support vector machine is used, the ratio of thedistance to an identification plane of the support vector machine from adata point, to the machine size of the support vector machine ispreferably used as the reliability of narrowing down of the intention(selected path) of the moving obstacle b seen from the host vehicle a.The illustrated moving obstacle b is any moving obstacle, and thedescribed content can be applied to various moving obstacles.

While the method of acquiring reliability is illustrated by using theprobability threshold process for the conflict tensor, and using theprobability threshold process and the support vector machine fornarrowing down the candidate path matrix, the present disclosure is notlimited thereto, and reliability may be acquired using other appropriatemethods.

The threshold θ can be used as an index of reliability. Specifically,when a relatively large value can be given to the threshold θ as atemporary value, the possibility of determining that there is apossibility of collision in calculation of the conflict tensor isdecreased, and the candidate paths are smoothly narrowed down. Thus, theintention decision and the behavior decision are relatively looselyperformed from the viewpoint of avoiding collision. That is, efficientpath selection is performed in the host vehicle. Even in the case of thepath selection, the behavior of another vehicle immediately before thethreshold process is probabilistically estimated in the same manner.Thus, the lowest reliability that appears during calculation is easilyassigned as the reliability of the path selection. Thus, when thereliability is sufficiently higher than the original reliability, andthe relatively loose intention decision and behavior decision areselected, it can be considered that the autonomous driving system 100can perform appropriate and efficient autonomous traveling. When thereliability is not sufficiently higher than the original reliability,the autonomous driving system 100 does not narrow down the candidatepaths of another moving obstacle, and selects relatively strictintention decision and behavior decision from the viewpoint of avoidingcollision based on the independent moving obstacle prediction thatassumes a plurality of candidate paths. Accordingly, the autonomousdriving system 100 can perform autonomous traveling having higherreliability.

Process of Narrowing Down Candidate Path Matrix

FIG. 4 is a flowchart illustrating a process of narrowing down thecandidate path matrix. The moving obstacle b will be described as atarget for path estimation.

As illustrated in FIG. 4 , in S80, the ECU 10 uses the third pathgeneration unit 17 to acquire the probability p of the moving obstacle btaking one candidate path (3.

The method of acquiring the probability p is described above.

In S82, the ECU 10 uses the third path generation unit 17 to determinewhether or not the probability p of the moving obstacle b selecting thecandidate path (3 is less than or equal to a threshold. The threshold isa value that is set in advance. When the ECU 10 determines that theprobability p of the moving obstacle b selecting the candidate path (3is less than or equal to the threshold (S82: YES), the ECU 10transitions to S84. When the ECU 10 determines that the probability p ofthe moving obstacle b selecting the candidate path (3 is not less thanor equal to the threshold (S82: NO), the ECU 10 transitions to S86.

In S84, the ECU 10 uses the third path generation unit 17 to substituteR_(bβ) with zero in the candidate path matrix R. Then, the ECU 10finishes the current process. In S86, the ECU 10 uses the third pathgeneration unit 17 to substitute R_(bβ) with one in the candidate pathmatrix R. Then, the ECU 10 finishes the current process.

Detection of Moving Obstacle Having Significant Influence

Hereinafter, detection of a moving obstacle having a relativelysignificant influence in path generation will be considered. A largenumber of moving obstacles are observed by the autonomous driving system100. When autonomous driving is performed, the prediction error tends tobe increased as the moving obstacle is far from the host vehicle. Thus,although it is not particularly limited, it is preferable not to reflectthe presence of the far moving obstacle in control of the autonomousdriving system 100. In order to realize a practical autonomous drivingsystem 100, it is desirable to establish a method of selecting a movingobstacle having a relatively significant influence from the large numberof moving obstacles.

A reconfigured outside-vehicle environment E(s) is mathematicallyrepresented in General Formula (53).p^(*)(τ, ĥ)=arg_(min){Cosdt(p(τ, ĥ),E(s))}  . . . (53)

In General Formula (53), p(τ) denotes a candidate path, and E(s) denotesthe outside-vehicle environment that is reconfigured in afour-dimensional time space from the sensor signal s. The estimatedvalue of the attitude (direction) of the host vehicle is denoted by ĥ.

When the host vehicle is denoted by a, and an environment (E(s)⊖Ob(s))acquired by removing a moving obstacle Ob(s) from the outside-vehicleenvironment E(s) is considered, a candidate path for the environment isacquired as in General Formula (54).p_(a) ^(⊖b)(τ)=arf_(min){Cost(p_(a)(τ),E(s)⊖Ob (s) )}  . . . (54)

When General Formula (55) is satisfied, the output of the autonomousdriving system 100 is not changed even when the moving obstacle Ob(s) isconsidered not to exist. Thus, the influence of the moving obstacleOb(s) on the autonomous driving system 100 may be considered relativelylow.p_(a) ^(⊖b)(τ)˜p_(a) ^(*)(τ)   . . . (55)

The difference between two candidate paths is evaluated using GeneralFormula (56). Furthermore. General Formula (57) is considered.

$\begin{matrix}{{d\left( {{p_{a}^{\ominus b}(\tau)},{p_{a}^{*}(\tau)}} \right)} = {d\tau{❘{{p_{a}^{\ominus b}(\tau)} - {p_{a}^{*}(\tau)}}❘}^{2}}} & (56)\end{matrix}$ $\begin{matrix}{F_{a} = {\sum\limits_{b}{d\left( {{p_{a}^{\ominus b}(\tau)},{p_{a}^{*}(\tau)}} \right)}}} & (57)\end{matrix}$

General Formula (56) and General Formula (57) are referred to as thedegree of environmental dependence of the autonomous driving system.

When the number of moving obstacles is denoted by n, the variance of thedifference in candidate path is defined as in General Formula (58), andGeneral Formula (59) is defined as a relative influence degree thatindicates the relative value of the influence of the moving obstacle bon the host vehicle a.

$\begin{matrix}{\sigma_{da}^{2} = {\frac{1}{n}{\sum\limits_{b}{d\left( {{p_{a}^{\ominus b}(\tau)},{{p_{a}^{*}(\tau)} - {\frac{1}{n}F_{a}}}} \right)}^{2}}}} & (58)\end{matrix}$ $\begin{matrix}{F_{ab}^{N} = \frac{d\left( {{p_{a}^{\ominus b}(\tau)},{p_{a}^{*}(\tau)}} \right)}{F_{a}}} & (59)\end{matrix}$

Such a quantity is a quantity that is acquired using the presence of themoving obstacle. Such a quantity has a low possibility that p*_(a)(τ) issignificantly changed when one object for which segmentation/trackingperformance is low is divided into two. Therefore, the autonomousdriving system 100 can be expected to acquire a stable result.

For example, it is considered that the degree of difficulty that theautonomous driving system 100 has in reading the outside-vehicleenvironment is estimated as in General Formula (60) using a relativeinfluence degree F.^(N) _(ab) described below.

$\begin{matrix}{{U_{a}(t)} = {\sum\limits_{b}{{❘{\delta{X_{b}(t)}}❘} \cdot F_{ab}^{N}}}} & (60)\end{matrix}$

It is considered that a moving obstacle α_(a) to which the host vehiclea should be alerted first is acquired using General Formula (61).α_(a)(τ)=arg_(max){|δX_(b)(τ)|·F_(ab) ^(N)}  . . . (61)

Effect of Autonomous Driving System (Trajectory Setting Device)

The autonomous driving system 100 (trajectory setting device 101)according to the present embodiment described thus far generates thefirst path of the host vehicle when all obstacles are assumed to bestationary obstacles, the second path of the host vehicle when themoving obstacle is assumed to move independently, and the third path ofthe host vehicle when the moving obstacle is assumed to move whileinteracting with at least one of the other obstacles or the hostvehicle. The autonomous driving system 100 calculates the reliability ofthe second path and the reliability of the third path, and sets thetrajectory of the host vehicle for traveling from the first path, thesecond path, and the third path based on the reliability of the secondpath and the reliability of the third path. Thus, the autonomous drivingsystem 100 can appropriately set the trajectory of the host vehicle fortraveling from paths that are generated using a plurality of differentmethods.

In the autonomous driving system 100, when the reliability of the thirdpath is higher than or equal to the third reliability threshold, thetrajectory setting unit 19 sets the trajectory of the host vehicle fortraveling from the third path. When the reliability of the third path islower than the third reliability threshold, and the reliability of thesecond path is higher than or equal to the second reliability threshold,the trajectory setting unit 19 sets the trajectory of the host vehiclefor traveling from the second path. When the reliability of the thirdpath is lower than the third reliability threshold, and the reliabilityof the second path is lower than the second reliability threshold, thetrajectory setting unit 19 sets the trajectory of the host vehicle fortraveling from the first path. Accordingly, when reliability issufficiently high in the autonomous driving system 100, the trajectoryof the host vehicle for traveling in the order of the third path and thesecond path can be employed. When the reliability of the second path andthe reliability of the third path are not sufficiently high in theautonomous driving system 100, the trajectory of the host vehicle fortraveling is set from the first path. Thus, a situation where thetrajectory of the host vehicle for traveling cannot be set due to theinsufficient reliability of the second path and the insufficientreliability of the third path is suppressed.

In the autonomous driving system 100, the reliability calculation unit18 calculates the reliability of the second path based on thereliability of sensing of the host vehicle and the reliability ofprediction of the candidate path of the moving obstacle in a case wherethe moving obstacle is assumed to move independently. Thus, thereliability calculation unit 18 can acquire the reliability of thesecond path more appropriately than when the reliability of the secondpath is calculated from merely one of the reliability of sensing of thehost vehicle or the reliability of prediction of the candidate path ofthe independent moving obstacle.

Similarly, in the autonomous driving system 100, the reliabilitycalculation unit 18 calculates the reliability of the third path basedon the reliability of sensing of the host vehicle and the reliability ofprediction of the candidate path of the moving obstacle in a case wherethe moving obstacle is assumed to move while interacting with at leastone of the other obstacles or the host vehicle. Thus, the reliabilitycalculation unit 18 can acquire the reliability of the third path moreappropriately than when the reliability of the third path is calculatedfrom merely one of the reliability of sensing of the host vehicle or thereliability of prediction of the candidate path of the interactivemoving obstacle.

While an exemplary embodiment of the present disclosure is describedthus far, the present disclosure is not limited to the embodiment. Thepresent disclosure can be embodied in various forms that are achieved bycarrying out various changes and improvements to the embodiment based onthe knowledge of those skilled in the art.

While the present embodiment describes the trajectory setting device 101as constituting a part of the autonomous driving system 100, thetrajectory setting device 101 does not need to constitute a part of theautonomous driving system. The trajectory setting device 101 mayconstitute a part of a driving assistance system that assists a drivingoperation of the driver. The trajectory setting device 101 may be usedin generation of a trajectory for guiding the driver in a navigationsystem. That is, the method of using the trajectory generated by thetrajectory setting device 101 is not particularly limited.

When the obstacle recognition unit 12 recognizes a plurality ofobstacles, the third path generation unit 17 may generate a comparativecandidate path for each candidate path generated as the third path. Thecomparative candidate path is a candidate path when one of the obstaclesis assumed not to exist. In such a case, the trajectory setting unit 19prohibits the trajectory of the host vehicle for traveling from beingset as a candidate path of which the degree of lateral separation fromthe comparative candidate path is less than or equal to a separationdegree threshold among the candidate paths generated as the third path.When a candidate path is significantly laterally changed in a case whereone obstacle is assumed not to exist, generation of the candidate pathis assumed to be unstable. Thus, the trajectory setting unit 19prohibits the trajectory of the host vehicle for traveling from beingset as the candidate path.

The degree of lateral separation between the candidate path and thecomparative candidate path can be set as the longest lateral distance bycomparing the lateral distance between the candidate path and thecomparative candidate path (distance in the width direction of thetraveling lane) for each longitudinal position in the traveling lane.The degree of lateral separation may be the integral value of thelateral distance in a certain number of longitudinal positions in frontof the host vehicle. The separation degree threshold is a value that isset in advance.

Calculation of the reliability by the reliability calculation unit 18 isnot limited to the content described above. The reliability calculationunit 18 may calculate the reliability of the second path or thereliability of the third path from merely the reliability of sensing ofthe host vehicle. The reliability calculation unit 18 may not calculatethe reliability of sensing of the host vehicle. The reliabilitycalculation unit 18 may calculate the reliability of the second pathfrom merely the reliability of the independent moving obstacleprediction, and may calculate the reliability of the third path frommerely the reliability of the interactive moving obstacle prediction.

The reliability calculation unit 18 may calculate the reliability of thefirst path based on the reliability of sensing of the host vehicle. Forexample, when the reliability of the second path is lower than thesecond reliability threshold, and the reliability of the third path isalso lower than the third reliability threshold, the trajectory settingunit 19 may request the driver to intervene when the reliability of thefirst path is lower than a first reliability threshold. The firstreliability threshold is a value that is set in advance.

The trajectory setting device 101 may not generate the first path. Thatis, the trajectory setting device 101 may not include the first pathgeneration unit 15 and include the second path generation unit 16 andthe third path generation unit 17. In such a case, the trajectorysetting device 101 generates the second path of the host vehicle whenthe moving obstacle is assumed to move independently, and generates thethird path of the host vehicle when the moving obstacle is assumed tomove while interacting with at least one of the other obstacles or thehost vehicle. The trajectory setting device 101 calculates thereliability of the second path and the reliability of the third path,and sets the trajectory of the host vehicle for traveling from thesecond path and the third path based on the reliability of the secondpath and the reliability of the third path. Thus, the trajectory settingdevice 101 can appropriately set the trajectory of the host vehicle fortraveling from paths that are generated using a plurality of differentmethods.

In such a case, when the reliability of the second path is lower thanthe second reliability threshold, and the reliability of the third pathis also lower than the third reliability threshold, the trajectorysetting device 101 may request the driver to intervene.

What is claimed is:
 1. A trajectory setting device that sets a trajectory of a host vehicle for traveling, the trajectory setting device comprising a processor configured to: recognize obstacles around the host vehicle; generate a first path of the host vehicle by assuming all of the obstacles to be stationary obstacles; detect a moving obstacle from the obstacles; generate a second path of the host vehicle when the moving obstacle is assumed to move independently; generate a third path of the host vehicle when the moving obstacle is assumed to move while interacting with at least one of the other obstacles or the host vehicle; and set the trajectory of the host vehicle for traveling from the first path, the second path and the third path based on an evaluation of the second path and the third path.
 2. A trajectory setting device that sets a trajectory of a host vehicle for traveling, the trajectory setting device comprising a processor configured to: recognize obstacles around the host vehicle; generate a first path of the host vehicle by assuming all of the obstacles to be stationary obstacles; detect a moving obstacle from the obstacles; generate a second path of the host vehicle when the moving obstacle is assumed to move while interacting with at least one of the other obstacles or the host vehicle; and set the trajectory of the host vehicle for traveling from the first path and the second path based on the an evaluation of the second path.
 3. The trajectory setting device according to claim 1, wherein the evaluation of the second path is based on reliability of sensing of the host vehicle and reliability of prediction of a candidate path of the moving obstacle when the moving obstacle is assumed to move independently.
 4. The trajectory setting device according to claim 1, wherein the evaluation of the third path is based on reliability of sensing of the host vehicle and reliability of prediction of a candidate path of the moving obstacle when the moving obstacle is assumed to move while interacting with at least one of the other obstacles or the host vehicle. 